I'm not sure if there is a way to explain this more precisely. Anyway, in Korean you probably don't put symbols in between, something else, but the point of both should be the same since there is no other way to change consonant sounds. At least I don't know any other ways.

I don't know Korean, but I got curious and looked on Google. This https://en.wikibooks.org/wiki/Korean/Essential_Pronunciation_Rules explains, but it's complicated. Reddit said tensed consonants are pronounced the same as lax consonants, but your throat literally pronounces with constricted muscles. http://www.101languages.net/korean/consonants.html said "Most Korean consonants come in three versions..."

"...namely unaspirated (without a puff of air), aspirated (with a puff of air) and tensed (stressed). Tensing isn't really found in English, but pronouncing the consonant quick and hard is a reasonable substitute." Maybe listen to pronunciations on YouTube?

It's when the singer is pronouncing words in an unnatural way that's hard to take seriously (over-exaggerated, singing too carefully so each word is understood by the listener, but ends up being pronounced/stressed incorrectly).

The way you pronounce a word is affected by the word before, after, the dialect, and the context. With singing, its more enunciated and sometimes pronounced differently(as i said, within the context) generally for more intelligibility.

Using a certain pronunciation is an artistic choice that lends to the singer's personality and/or the musical choices within the song.